function display_div (id_group,id_item)
{
    var items = document.getElementById(id_group).getElementsByTagName('div');

    for (var i=0; i<items.length ; i++)
    {
        if (id_group+i == id_item)
        document.getElementById(id_group+i).style.display ='block';
        else
        document.getElementById(id_group+i).style.display ='none';
    }
}